Business and Property Management Agreements with RMR LLC (Details) - RMR LLC $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) employee agreement	Mar. 31, 2016 USD ($)
Related Party Transaction [Line Items]
Number of employees | employee	0
Number of agreements | agreement	2
Related party expense	$ 2,704	$ 2,508
Reimbursement expense	3,391	2,944
Internal audit costs	67	67
Net Property Management and Construction Supervision Fees
Related Party Transaction [Line Items]
Related party transaction amount	$ 2,466	$ 2,109